Re: Decora HCPRF WAS: Re: UPB, etc. WAS: Need some antenna advice...

[nobody@xxxxxxxxxxxx (Dave Houston)]

The only error checking is the Manchester encoding wherein each 1 bit is 10
on the powerline and each 0 bit is 01 on the powerline. If you analyze it,
after the start code (1110) there's no way you can have a "legal" run of
more than 11 or 00 within the code. That's fairly robust. The probability
that a ~120kHz "noise" source will create such a pattern out of whole cloth
is nil.

I don't think there is a requirement that a 3 cycle silence precede a start
code. The second copy of the code follows without such a gap.

The likelihood of RF collisions that create valid codes is very, very, very
low. The RF codes also incorporate error checking. If two motion sensors see
the same motion, the transceiver will likely see a corrupted RF code and
will ignore it. The transceiver receives the RF, decodes it and then (if
it's OK) sends it to the powerline. There is no one-to-one correspondence
between the RF code bits and the PLC bits. Some transceivers will relay
certain commands that others do not - All Units On, All Lights On, All
Lights Off are not universal.

However, if you have multiple transceivers and multiple motion detectors you
might see some really complex behavior where one transceiver "hears" from
one motion sensor and another transceiver "hears" from another a few ms
later. That could cause PLC collisions. It all depends on the strength of
the RF signals (as seen at the transceivers) and the timing between when the
motion is detected by the sensors. The AGC/ATC in the RF receiver circuits
will pick out a stronger signal that overlays a weaker signal. The RF code
is about 105ms long. Once a valid code is being sent to the powerline, a
transceiver is deaf to RF until the PLC cycle completes but a stronger RF
code can override a weaker one if it starts before the first RF code
competes.

It's a shame that the Power Line Communication Bibliography disappeared. It
had links to some excellent white papers. I think all were stored on the
same server so they probably decided to free up some space. I wish I had
saved copies of a few key papers.

"Robert Green" <ROBERT_GREEN1963@xxxxxxxxx> wrote:

>"Dave Houston" <nobody@xxxxxxxxxxxx> wrote in message
>
>> Reading the docs, are we? Geesh - no wonder things are so confused. ;)
>
>I had to go through a bit of a search to get them, too.  I lost the little
>paper insert and then realized that the house and unit code are set via the
>programming button.  I didn't remember how to do that. (old age, I guess).
>Leviton never replied to support emails but I finally found the PDF imbedded
>in one of their catalogs (had to DL 60MB by modem to do it!).  The funny
>part is that I had finally found a use for HCPRF, but that was based on the
>mistaken assumption that it was a old-fashioned relay module like the TM751
>and RR501 and not a solid state relay for incandescent loads.  I was going
>to use it to control some fluorescent lights!  :-(  No such luck!   The one
>thing the module has going for it, as opposed to the TM751 is that it's
>silent.  My MIL finds the TM751's relay clacking objectionable.
>
>> I did not do extensive testing with the HCPRF. Once I saw there was no
>room
>> to add an external antenna jack, I lost interest.
>
>Too bad.  I can afford to experiment on mine and might have taken a whack at
>modifying it just out of curiosity.  It's definitely not happy within my
>current setup.
>
>> What unit codes are you seeing the strange behavior on?
>
>On a number of different codes.  B13 is the most popular inadvertent turn on
>(and off) but others do it as well.  I should add that these units are
>controlled by the infamous Hawkeye PIRs.  As I wrote that, I realize I may
>have blown a couple of 100 bucks on the Lynx.  The collisions may be
>occurring in the RF portion of the "control sequence."  :-(   I used to keep
>the CM11A active, just logging the weird signals but I stopped using it when
>it started showing signs of overheating.
>
>> www.mbx-usa.com/multiples.htm gives a very brief summary of what you'll
>see
>> with multiple transceivers.
>
>Yes, I've been spending a lot of time there, sifting through the diagrams
>and data.
>
>Am I right in assuming that there's no error checking like a CRC check of
>the *complete* X-10 signal?  I see it as a series of 120KHz tones
>synchronized to the zero crossing.  When a receiver sees 3 or more tone-free
>AC cycles it is then "primed" to look for a "start code" of  "1110" which,
>for a standard X-10 transmitter, is a series of 9 pulses, total.  Six of
>those pulses are ignored, as they are for split phase systems zero
>crossings.  The Powerlinc appears to differ in that it only sends pulses on
>one phase, so the scope trace looks a lot like the actual binary string
>transmitted.
>
>My understanding is that whatever error checking occurs, it's in
>representing a 4 bit binary number like 1001 in 8 bits using a bit's
>complement to guard against errors.  So 1001 would become 10010110.  The
>only place this does NOT occur is in the start code, which is just 1110 that
>follows at least three signal-free AC cycles.
>
>FWIW, I can't seem to reach the Power Line Communication Bibliography
>referenced on http://www.mbx-usa.com/x10-sig.htm
>I don't know whether it's me or they've disappeared.  I searched the Wayback
>machine for it:
>
>http://web.archive.org/web/20040606020312/http://info.iet.unipi.it/~filippo/
>documenti/powerlines/PowerLineCom/FrameRIF.html
>
>otherwise known as http://tinyurl.com/8ghye
>
>and I can retrieve the bibliography list, but the URLs they refer to are
>gone, too.  I've tried to pull them one at a time out of the Wayback and
>then tried using Google to see if the site's simply been relocated but I
>can't seem to find a new version of the site.  :-(